Apparatus for generating high frequency oscillations



Oct. 12, 1943. w. s. PERCIVAL 2,331,723

APPARATUS FOR GENERATING HIGH FREQUENCY OSCILLATIONS Filed Dec. 1, 1938 INVENTORJ WILLIAM SP NCER PERCI VAL A TTORNEK ably shaping said Patented Oct. 12, 1943 APPARATUS FOR GENERATING HIGH FREQUENCY OSCILLATIONS William Spencer Percival, Ealing, London, England, assignor to Electric & Musical Industries Limited, Hayes, England, a company of Great Britain Application December 1,

In Great Britain December 2,

9 Claims.

This invention relates to apparatus for generating high frequency oscillations and is concerned more particularly with apparatus for generating higher frequencies than can be generated by the usual thermionic valve circuit "arrangements owing, among other things, to the gird and plate capacities of the valves.

It has previously been proposed to employ cathode ray tube apparatus for the generation of very high frequencies and in such apparatus it has been proposed to employ a collecting electrode upon which the electron beam impinges after being subjected to deflection and interception by an apertured electrode. One of the main ing said beam towards a target electrode which is resonant at the oscillation frequency to be generated and deflecting said beam over a surface which serves to intercept the beam intermittently before it impinges upon said target, and wherein in order to raise the impedance of said target its radiation resistance is reduced by the provision of a shielding member or by suittarget. The surface which serves to intercept the beam intermittently may be a member formed with apertures through which the beam passes successively due to de-, flection, before impinging upon the target, the frequency of the oscillations generated being determined by the number of apertures. in the member and the speed of deflection from one aperture to the next. The target may constitute the extremity of the central core of a coaxial conductor or it may be an elongated member which is bent back upon itself so as to form a short resonant transmission line. Again auxiliary elements may be arranged in close proximity to the target in order that its radiation resistance may be low compared with that of a dipole aerial.

In order that the invention may be more 1938,:Serial No. 243,362

clearly understood and readily carried into effect, some alternative forms of high frequency generating apparatus will now be described by way of example with reference to Figures 1, 2 and 3 of the accompanying drawing.

Referring to Figure 1, parts of an electrode system of a cathode ray tube T are shown including a cathode l, the electrons from which are formed into a beamZ by an electron gun not shown in the drawing. The beam is deflected at a high speed in a circular path by two pairs of deflecting plates 3, 3arranged at right angles. A sinusoidal voltage is applied to one pair of plates and another sinusoidal voltage having a phase displacement of with respect to the first is applied to the other pair of plates. The

deflected beam impinges upon'a circular member 4 having apertures 5 formed near its periphcry. The deflected beam passes through the apertures in turn and is focused by a coil C upon a taget or collector electrode ,6. The focus sing arrangements ideally would be such that th'e'beam is focussed in the apertures 5 and'also at the target 6, but as this is difficult to achieve in practice, the voltages applied to the electrodes of the electron gun are such that the beam would be in the absence of the focussing coil C, have its focal point in the plane D-E shown in dottedlines, midway between the disc 4 and target 6, the loss from accurate focussing being insignificant. The electrode 6 thus receives charges at regular intervals, the frequency being" equal tothe frequency of rotation of the beam multiplied by the number of apertures in the member 4. For example,'if the frequency of theirotation of the electron beam is Mc./s and there are 50 apertures in the member 4, the oscillation frequency generated will be 5,000 Mc./s.

The target or collector electrode 6 may form part of a resonant circuit which may either be bent back on itself as shown in Figure 1 or otherwise rendered substantially nonradiating by being formed into shapes known to those skilledin'the art. It may, of course, consist of more than one vhalf wavelength. Auxiliary elements may beprovided for the purpose of reducing the radiation of the target '6, the fundamental object always being to reduce the radiation resistance. The electron beam should impinge on the point in the target at which the impedance is highest, or if it isfound that a sufficient impedance can be obtained, at a point at which the impedance is equal to the optimum load resistance for the cathode ray tube considered as a valve.

Provision may be made to enable the field which focusses the electron beam onto the target 6 to bevaried in such a manner that the point quency to be generated and means for deflecting said beam over a surface which serves to intercept the beam intermittently before it strikes said target electrode, said target being of predetermined length and bent back upon itself to be substantially non-radiating.

4. In an oscillation, generator, an, electron discharge device having an electron gun, horizontal and vertical beam deflecting electrodes 9.

effective when suitably energized to produce rotarybeamdeflection, an electrode having a plurality of apertures concentrically spaced so as to tor 9 by a transmission line transformer. In or- 7 other convenient means. 7 the end of the conductor which forms the target electrode 1 or is connected to that electrode should be a point of high impedance for example, Zr andbe coupled to the main portion of the transmission line of the impedance Z by a suitable length, for example, a quarter of a wavelength of impedance Z: such that Zt ==ZoZL An arrangement similar. to Figure 2 is shown in Figure 3 but-in thisv case the quarter wavelength conductor I0 is connected to the sheath lat a point I l, and is tapped at a suitable point by. the main conductor 9.

In either of the arrangements shown in Figures 2 or. 3 the main conductor may be connected directly with a suitable aerial for example, a dipole.

" I claim:

1. Apparatus for generating high frequency oscillations comprising an evacuated envelope, a source of electrons and a target electrode mounted-Within said envelope, means for projecting a beam of said electrons towards said tar et electrode, an orificed member, means for deflecting said beam over asurface of said member which serves to intercept the beam intermittently, and means for causing certain of the electrons to strikea focal spot on said target electrode where its impedance is of an optimum value in relation to an external load resistance connected thereto, said target electrode and its mounting being further characterized in that they form a resonant circuit entirely within said envelope, said resonant circuit being tuned to the frequency of oscillations generated by the intermittent impacts of electrons on said target electrode, and constituting means for minimizing the dissipation of energy by radiation.

2. Apparatus for generating high frequency oscillations comprising a source of electrons, means for forming said electrons into a beam and for Projecting said beam towards a target electrode which is resonant at the oscillation frequency to be generated and has relatively high impedance, and means for deflecting said beam over a surface which serves to intercept the beam intermittently before it strikes said target electrode, said target forming the extremity of the central coreof a coaxial conductor'system, said target electrode being of a high impedance Z1 and coupled to the main portion of a transmission line of impedance Z0 by a length of conductor of impedance Zt such that Z? equals Z021.

3. Apparatus for generating high frequency oscillations comprising a source of electrons, means for forming said electrons into a beam and for projecting said-bearntowards a target electrod whichds esonant t heo at n i In this arrangement alternately intercept and pass electrons therethrough-in accordance with said rotary beam deflection, an electron collector electrode, said electrodes being arranged in the order named, said collector electrode, being so constructed and mounted. that it, together with its mounting, forms a resonant circuit tuned to the frequency of oscillations generated by the intermittent transit of electrons through said apertures, and means for rendering said. collectorelectrode substantially non radiating, thereby to giveit a relatively high impedance value.

5. In an oscillation generator, an electron discharge device having an electrongun, horizontal and vertical beam deflecting electrodes, an electrode having a plurality of apertures concentrically spaced so as to alternately intercept and pass electrons therethrough, and a; resonant electron collector electrode; said electrodesbeing arranged in the order named; saidcoll-ectorelec trode having an overall length'equal to an even multiple of one-quarter wavelength, said collector being folded back upon itself to render the same substantially non-radiant.

6. In an oscillation generator, an electron dischargedevice havingan electron gun, horizontal and vertical beam deflecting electrodes, anelectrode having 'a plurality" of apertures concen trically spaced so as to alternately intercept and pass electrons therethrough, anelectron collector electrode, said electrodes being disposed" in the order named, said collector electrodeconstitutingat least a portion of aresonant'circuit and forming an extension of the inner conductor-ofa-coaxial conductor-system-,- and means constituted by a portion of said outer conductor whereby: said collector is surrounded and renderedisubstam tially non-radiant.

7. In a cathode ray device, means forproducing a focussed-electron beam, means for.rotatively deflecting said-beam, means-in the rotary path of said beam for intercepting.the-same at evenly spaced positions, an. electron collector electrode positioned-to receive. a portion of said beam which is-not intercepted, a sheath; around saidcollector, said: collector" having, such length that it together with said sheathzforms-aaresoe nant and non-radiant system.

8. In acathode ray.device,means includingan electron gun and. a magnetic beam focussingder; vice for producing. a guidedfbeam a coaxialconductor system-eatargetgelcctrode within the-outerconductor of, said.coaxial system;v and a connec: tion from saidgtarget electrode to the-innercom ductor .of said coaxial system, said-connectionbeing one-quarter of a wavelengthlong, whereby saidtarget isapolnt of high-impedance for-elece trons ofsaid beam which impinge .thereom 9.- Apparatus of the class-described.comprising acathode ray-tubehaving an;e1ectr,on gun, beam deflecting electrodes,v an ,orificedelectrode portions of which are so disposed as to-,intermit;-' tently intercept. the. electron beam ,when the said tube a resonant circuit whose frequency characteristic is tuned to the periodicity at which said beam traverses the series of orifices in said orificed electrode, said target electrode and its support possessing an impedance value which substantially matches that of a load connected thereto externally of said tube.

WILLIAM SPENCER PERCIVAL. 

